Power monitors are devices that measure and output the energy consumption of an apparatus that is powered from an electric outlet or socket (referred to herein as an “electric appliance” or simply an “appliance”). Power monitors can be used in a number of ways to measure the energy consumption of any number of electric appliances. They can be used, for example, to measure the power consumption of appliances such as computers, televisions, kitchen appliances, and so on.
As is shown in FIG. 9, a power monitor typically takes the form of an electrical device that plugs into an electrical socket or outlet, and can include a built-in electric outlet into which can be plugged the appliance. A power monitor typically includes a display unit to locally display parameters of interest to the user. The display unit integrated into the plug portion or tethered thereto, as is shown in FIG. 9. These parameters can include instantaneous power, total energy consumption, cost, and carbon dioxide (CO2) emissions. The latter two parameters require a conversion factor from energy to cost per kiloWatt-hours and kilogram of CO2 per kiloWatt-hours be input into the device. To select between these various types of information on a display unit, power monitors typically contain a simple user interface composed of buttons to select between modes and input information.
In principle, power monitors interrupt the conduction path between the device and electrical socket or outlet. Power monitors measure the AC voltage on the electrical socket and measure the current flowing into the device via the interrupted current path. The current may be measured using an accurate and precise power resistor in series with the device and electrical socket, by measuring the voltage across this resistor. An electrical circuit is designed to convert the AC voltage on the electrical socket and produce a DC voltage to provide power to the remaining electronics in the power monitor. The remaining electronics may include an analog-to-digital converter, a microprocessor, display unit, and buttons. The analog-to-digital converter converts the voltage across the resistor into a digital signal that is input into the microprocessor. The microprocessor stores this information and converts it with the measured AC voltage into power and displays it on the display unit. The microprocessor may further integrate this power to produce energy, and can optionally provide a conversion to cost and or consumption of CO2.
It is typically challenging to measure the complete consumption with device-level granularity in a home or commercial building using one or more power monitors. Without wireless communications, a user will typically plug their power monitor into a number of devices or surge protectors or power strips in their home serially to obtain a comprehensive picture of power consumption. This choice is limited by the size of the power monitor or cost, they are typically larger than the vertical spacing of outlets. These are also the same issues with a number of power monitors including wireless communications.